Positive electrode active material particle powder for non-aqueous electrolyte secondary battery, method for producing same, and non-aqueous electrolyte secondary battery

ABSTRACT

Positive electrode active material particle powder includes lithium manganese oxide particle powder having Li and Mn as main components and a cubic spinel structure with an Fd-3m space group. The lithium manganese oxide particle powder is composed of secondary particles, which are aggregates of primary particles, an average particle diameter (D50) of the secondary particles being from 4 μm to 20 μm, and at least 80% of the primary particles exposed on surfaces of the secondary particles each have a polyhedral shape in which each (111) plane thereof is adjacent to at least one (100) plane thereof.

TECHNICAL FIELD

The present invention relates to positive electrode active materialparticle powder for non-aqueous electrolyte secondary batteries, methodsfor producing same, and non-aqueous electrolyte secondary batteries.

BACKGROUND ART

With the spread of mobile devices in recent years, secondary batteriesare being widely used. Among them, lithium ion secondary batteries,which are characterized by high charging/discharging voltage and largecharging/discharging capacity, have attracted attention.

Conventionally, as positive electrode active material in a 4 V classhigh energy lithium ion secondary battery, spinel type structureLiMn₂O₄, layered rock salt type structure LiCoO₂, LiCo_(1-x)Ni_(x)O₂,LiNiO₂, and the like are generally known. Among these, LiCoO₂ excels inthat it has a high voltage and high capacity, but the supply amount ofcobalt material is small, leading to increased production cost, andthere is also a problem from the viewpoint of environmental safety ofwaste batteries after use.

On the other hand, research into spinel structure lithium manganeseoxide (basic composition: LiMn₂O₄) is thriving, because a large supplyamount can suppress increases in cost, and manganese having goodenvironmental suitability is used. Further, in a layered rock salt typestructure of positive electrode active material, diffusion paths of Liare two-dimensional, whereas in a spinel structure of positive electrodeactive material, diffusion paths of Li are three-dimensional, which isof interest in positive electrode active material for secondarybatteries, particularly for vehicular applications and stationaryapplications.

Here, when high crystallinity is developed in order to obtain highbattery performance, obtained lithium manganese oxide particles have anoctahedral structure that is the idiomorphic form of a cubic spinelstructure, and dissolution of Mn is likely to occur. Further, in asecondary battery using such a positive electrode active material,problems occur such as inferior charge/discharge cycle properties andstorage properties at high temperatures.

Varied research and development (Patent Literature 1-5) has beenundertaken to solve the problems of non-aqueous electrolyte secondarybatteries using such lithium manganese oxide spinel structure positiveelectrode active material.

CITATION LIST Patent Literature

-   [Patent Literature 1] Japanese patent 4114314-   [Patent Literature 2] Japanese patent 3375898-   [Patent Literature 3] Patent application publication JP 2002-145617-   [Patent Literature 4] Japanese patent 5344111-   [Patent Literature 5] Japanese patent 5435278

SUMMARY OF INVENTION Technical Problem

However, conventional technology, including the technology proposed inPatent Literature 1 to 5, cannot be said to be sufficient forconstituting a non-aqueous electrolyte secondary battery that excels inhigh temperature performance.

The present invention has been achieved in view of such problems, and anaim thereof is to provide positive electrode active material particlepowder for a non-aqueous electrolyte secondary battery, a method forproducing same, and a non-aqueous electrolyte secondary battery, whichexcel in high temperature performance.

Solution to Problem

Positive electrode active material particle powder for a non-aqueouselectrolyte secondary battery pertaining to one aspect of the presentinvention is positive electrode active material particle powdercomprising: lithium manganese oxide particle powder having Li and Mn asmain components and a cubic spinel structure with an Fd-3m space group,wherein the lithium manganese oxide particle powder is composed ofsecondary particles, which are aggregates of primary particles, anaverage particle diameter (D50) of the secondary particles being from 4μm to 20 μm, and at least 80% of the primary particles exposed onsurfaces of the secondary particles each have a polyhedral shape inwhich each (111) plane thereof is adjacent to at least one (100) planethereof.

Advantageous Effects of Invention

The positive electrode active material particle powder for a non-aqueouselectrolyte secondary battery pertaining to the above aspect excels inhigh temperature properties. Thus, it is suitable as a positiveelectrode active material of a non-aqueous electrolyte secondary batterythat has excellent charge/discharge cycle properties and storageproperties at high temperatures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a scanning electron microscope (SEM) image showing outerappearance of aggregated secondary particles pertaining to example 1,and FIG. 1B is an SEM image showing outer appearance of aggregatedsecondary particles pertaining to comparative example 1.

FIG. 2A is an enlargement of a portion of an SEM image of an outerappearance of aggregated secondary particles pertaining to example 1;FIG. 2B schematically shows structure of a primary particle; FIG. 2C isan enlargement of a portion of an SEM image of an outer appearance ofaggregated secondary particles pertaining to example 5; and FIG. 2Dschematically shows structure of a primary particle.

FIG. 3A is an enlargement of a portion of an SEM image of an outerappearance of aggregated secondary particles pertaining to comparativeexample 1 and FIG. 3B schematically shows structure of a primaryparticle.

FIG. 4 is an SEM image of an outer appearance of aggregated secondaryparticles pertaining to comparative example 2.

FIG. 5 shows an X-ray diffraction (XRD) of aggregated secondaryparticles pertaining to example 1.

FIG. 6 schematically shows a method for producing aggregated secondaryparticles pertaining to an embodiment.

FIG. 7 is a schematic cross section showing configuration of anon-aqueous electrolyte secondary battery 100 pertaining to anembodiment.

FIG. 8A shows high temperature storage properties of non-aqueouselectrolyte secondary batteries pertaining to example 1 and comparativeexample 1, and FIG. 8B shows high temperature cycle properties.

FIG. 9A is an SEM image showing an LMO crystal that has a (100) planeand (111) planes, and FIG. 9B is an SEM image after a corrosion(etching) test.

EMBODIMENT

[Developments Leading to Present Invention]

In the course of arriving at the present invention, the inventorsconducted the following investigation.

(1) Mn Dissolution and High Temperature Properties Under HighTemperature Environment

Degradation of charge/discharge cycle properties and storage propertiesunder a high temperature environment is attributable to: (i)deterioration of crystal lattice due to desorption/insertion behavior oflithium ions in the crystal structure of positive electrode activematerial accompanying repetition of charging/discharging, which expandsand contracts crystal volume, destroying the crystal lattice; (ii)instability of crystals in a state when lithium of lithium manganeseoxide is halfway charged in a certain charged state; (iii) deteriorationof current collection of an electrode; (iv) occurrence of Mn dissolutionin electrolytic solution; and the like. Here, Mn dissolution isconsidered to be caused by a disproportionation reaction as shown below.2Mn³⁺(spinel)→Mn⁴⁺(spinel)+Mn²⁺(in electrolytic solution)

(2) Suppression of Crystal Plane and Mn Dissolution

The inventors considered that dissolution of Mn is more likely to occurin a crystal structure having sharp edges and apexes such as anoctahedral shape, since Mn dissolution occurs more frequently at highcurvature locations in particles. Therefore, in order to suppressdissolution of Mn, the inventors found that it is important that crystalplanes adjacent to a (111) plane are adjacent to crystal planes otherthan a (111) plane, in order to reduce curvature and apex of a ridgeformed by crystal planes in primary particles.

Further, they found that degree of Mn dissolution varies depending on adifference in crystal planes exposed on particle surfaces. That is, theyfound that (100) planes and (110) planes can suppress Mn dissolutionmore than (111) planes.

Note that in this description and claims, the term “(111) plane”includes any planes equivalent to a (111) plane. That is, eight planesincluding a (-111) plane, a (1-11) plane, and a (11-1) plane.

“(100) plane” also means any planes equivalent to a (100) plane. Thatis, six planes including a (010) plane, a (001) plane, and a (-100)plane. Further, “(110) plane” also means any planes equivalent to a(110) plane. That is, twelve planes including a (101) plane, a (011)plane, and a (-110) plane.

In description of crystal planes, “-1” is supposed to be written so the“-” is a bar above the “1”, but in the present description, “-1” iswritten for convenience.

In the following description, unless otherwise specified, whendescribing a (100) plane, a (110) plane, a (111) plane, or the like,equivalent planes are intended to be included.

(3) Measures to Reduce (111) Planes

The reason a cubic manganese spinel crystal is likely to form theidiomorphic octahedral shape composed of (111) planes and planesequivalent thereto is considered to be because the crystal plane growthrate of a (111) plane is lower than that of other crystal planes (forexample, (100) plane, (110) plane, and (221) plane). Conversely, sincethe crystal plane growth rates of (100) planes and (110) planes aregreater than that of (111) planes, growth of crystal planes other than(111) planes is promoted in the process of crystal growth, and as aresult, these crystal planes disappear.

Accordingly, it was found that if it is possible to lower crystal planegrowth rate of planes other than (111) planes, in particular (100)planes and (110) planes, and to suppress growth of crystal planes, acrystal having these planes can be obtained.

[Aspects of the Present Invention]

The positive electrode active material particle powder for a non-aqueouselectrolyte secondary battery pertaining to one aspect of the presentinvention is positive electrode active material particle powdercomprising: lithium manganese oxide particle powder having Li and Mn asmain components and a cubic spinel structure with an Fd-3m space group,wherein the lithium manganese oxide particle powder is composed ofsecondary particles, which are aggregates of primary particles, anaverage particle diameter (D50) of the secondary particles being from 4μm to 20 μm, and at least 80% of the primary particles exposed onsurfaces of the secondary particles each have a polyhedral shape inwhich each (111) plane thereof is adjacent to at least one (100) planethereof.

In the above embodiment, “a polyhedral shape in which each (111) planethereof is adjacent to at least one (100) plane thereof” indicates apolyhedral shape in which ridges are formed by flat crystal planesabutting each other. Here, “ridges” may overlap in a way that crystalplanes are known.

Positive electrode active material particle powder for a non-aqueouselectrolyte secondary battery pertaining to another example isconfigured so that one or more metal elements other than Mn aresubstituted at an Mn(16d) site, and when Me denotes a metal elementother than Li among the one or more metal elements, an [Li/(Mn+Me)]ratio is from 0.5 to 0.65.

Further, positive electrode active material particle powder for anon-aqueous electrolyte secondary battery pertaining to another exampleis configured so that, in X-ray diffraction analysis, a cubic spinelphase based on Li and Mn, and a phase of one or more other compounds arepresent.

Further, a non-aqueous electrolyte secondary battery pertaining toanother aspect of the present invention comprises: a positive electrodeelement that includes the positive electrode active material particlepowder pertaining to any one of the examples described above.

Further, a method of producing positive electrode active materialparticle powder for a non-aqueous electrolyte secondary batterypertaining to another aspect of the present invention is a methodcomprising: mixing trimanganese tetroxide, a lithium compound, and acrystal plane growth suppressor to form a mixture, and firing themixture in an oxidizing atmosphere at a temperature from 700° C. to 950°C.

The method of producing positive electrode active material particlepowder for a non-aqueous electrolyte secondary battery pertaining toanother example is configured so that the trimanganese tetroxide iscomposed of secondary particles, which are aggregates of primaryparticles, an average particle diameter (D50) of the secondary particlesbeing from 3 μm to 20 μm, and crystallite size of the primary particlesbeing from 50 nm to 150 nm.

Further, the method of producing positive electrode active materialparticle powder for a non-aqueous electrolyte secondary batterypertaining to another example is configured so that the crystal planegrowth suppressor is a niobium compound. Note that substances other thana niobium compound are not excluded as the crystal plane growthsuppressor.

Further, the method of producing positive electrode active materialparticle powder for a non-aqueous electrolyte secondary batterypertaining to another example is configured so that the crystal planegrowth suppressor is a molybdenum compound. Note that in this examplealso, substances other than a molybdenum compound are not excluded asthe crystal plane growth suppressor.

Hereinafter, examples for implementing the present invention aredescribed with reference to the drawings.

Note that the following configuration is an example used for describingstructures of the present invention and actions and effects exerted bythe configuration in an easy-to-understand manner, and aside fromessential elements thereof, the present invention is not limited to theexample described below.

[Embodiment]

1. Outline of Structure of Positive Electrode Active Material ParticlePowder

An outline of structure of positive electrode active material particlepowder pertaining to the present embodiment is described below.

The positive electrode active material particle powder pertaining to thepresent embodiment is primarily composed of lithium (Li) and manganese(Mn), and is lithium manganese oxide having a cubic spinel structure ofspace group Fd-3m (stoichiometric composition: LiMn₂O₄). However, thepositive electrode active material particle powder pertaining to thepresent embodiment is not limited to the stoichiometric compositionabove, and as long as the crystal structure is maintained, cations aredeficient or excessive, or it is also possible to have a composition inwhich oxygen ions are deficient or excessive.

In the positive electrode active material particle powder pertaining tothe present embodiment, a part of Mn may be partially substituted withcations of another metal element (for example, one or more metalelements selected from metal elements that can be substituted at the 16dsite such as Li, Fe, Ni, Mg, Zn, Al, Co, Cr, Si, Ti, Sn, V, or Sb).

2. Crystal Plane Growth Suppression

The positive electrode active material particle powder pertaining to thepresent embodiment is formed into a desired shape by using a niobium(Nb) compound or a molybdenum (Mo) compound, for example, as a crystalplane growth suppressor. Added amounts of crystal plane growthsuppressor such as Nb or Mo is preferably in a range of 0.001 to 0.012in terms of molar ratio of metal substitute to Mn.

3. Ratio of Li/(Mn+Me)

In the positive electrode active material particle powder pertaining tothe present embodiment, a ratio of Li/(Mn+Me) is preferably 0.5 orgreater. This is because internal resistance can be reduced and crystalstructure strengthened when compared to a stoichiometric composition ofLiMn₂O₄, to further improve properties as a positive electrode activematerial of a non-aqueous electrolyte secondary battery with excellenthigh temperature properties.

For example, Li(Li_(x)Mn_(2-x))O₄ (where x is a substitution amount) inwhich a part of Mn is substituted with Li, Li(Li_(x)Al_(y)Mn_(2-x-y))O₄(where x and y are substitution amounts) in which a part of Mn issubstituted with Al and Li, and the like, can be used. Note that adesired Li/(Mn+Me) ratio is from 0.50 to 0.65, and more preferably from0.53 to 0.63.

4. Crystal Planes

Primary particles of the positive electrode active material particlepowder pertaining to the present embodiment have shapes as shown in FIG.1A and FIG. 2A. That is, as shown in FIG. 2B, a polyhedron shape inwhich a (111) plane is adjacent to at least one (100) plane.

Note that such a crystal structure can be realized by suppressing growthof crystal planes other than (111) planes in the process of crystalgrowth. That is, such a structure can be realized by retaining a planethat disappears in the course of normal crystal growth.

On the other hand, as shown in FIG. 1B, FIG. 3A, and FIG. 4 where anamount of primary particles for which crystal growth is suppressed isless than 80%, octahedral particles that are the idiomorphic form oflithium manganese oxide become composed of (111) planes as a result ofgrowth rate of (111) planes being slower than that of other crystalplanes.

In the positive electrode active material particle powder pertaining tothe present embodiment, as long as high temperature storage propertiesand high temperature cycle properties are in a range achievingexcellence as a non-aqueous electrolyte secondary battery, primaryparticles having octahedral, particular, and other shapes may beincluded. It suffices that at least 80% of the number of primaryparticles visible on surfaces of aggregated secondary particles such asshown in FIG. 1A have a polyhedral shape in which each (111) plane isadjacent to at least one (100) plane, as shown in FIG. 2B.

5. Primary Particle Diameter and Secondary Particle (Aggregate Particle)Diameter

Average primary particle diameter of positive electrode active materialparticle powder pertaining to the present embodiment is from 0.3 μm to 5μm, preferably from 0.4 μm to 4 μm, and more preferably from 0.5 μm to 3μm.

Average secondary particle diameter (D50) is from 4 μm to 20 μm.Excellent high temperature performance as a secondary battery can beobtained by controlling average secondary particle diameter to the aboverange.

According to the present embodiment, average primary particle diameterwas observed using a scanning electron microscope with energy dispersiveX-ray analyzer (SEM-EDX) (manufactured by Hitachi High-TechnologiesCorporation) and an average value read from an SEM image.

Further, average secondary particle diameter (D50) is a volume-basedaverage particle diameter measured by a wet laser method using a laserparticle size distribution measuring apparatus Microtrac HRA(manufactured by Nikkiso Co., Ltd.).

6. Specific Surface Area by BET Method

Specific surface area of a positive electrode active material particlepowder pertaining to the embodiment according to the BET method is from0.1 m²/g to 1.2 m²/g. When specific surface area according to the BETmethod is less than 0.1 m²/g, growth of primary particles proceedsexcessively, which is considered to lead to a decrease in stability. Onthe other hand, when specific surface area according to the BET methodexceeds 1.2 m²/g and primary particles that are too small (primaryparticle diameter is smaller than desired) become an aggregatedsecondary particle body, the aggregated secondary particle is unable tomaintain a framework, and properties as a positive electrode activematerial become unstable.

Specific surface area according to the BET method is preferably from0.15 m²/g to 0.8 m²/g, and more preferably from 0.2 m²/g to 0.75 m²/g.

7. Other Properties

A lattice constant of the positive electrode active material particlepowder pertaining to the present embodiment is from 0.8185 nm to 0.8225nm.

Further, as shown in FIG. 5, for example, in X-ray diffraction (XRD) ofthe positive electrode active material particle powder pertaining to thepresent embodiment, aside from lithium manganese oxide that can beindexed by Fd-3m, niobium as a crystal growth suppressor may exist,combined with Li, in a phase containing LiNbO₃.

For X-ray diffraction, measurement was carried out using SmartLab(manufactured by Rigaku Corporation) (source: CuKα), and measurementconditions were 10° to 90° in 2θ/θ by 0.02° steps (1.2 s hold scan) at0.02° increments. Further, when obtaining lattice constant information,a standard powder of Si was used as an internal standard substance andcalculation performed by using the Rietveld method.

8. Method of Producing Positive Electrode Active Material ParticlePowder

A method of producing positive electrode active material particle powderpertaining to the present embodiment is described below, with referenceto FIG. 6.

(i) First, a lithium compound, trimanganese tetroxide, and a crystalplane growth suppressor are mixed in a ball mill (step S1).

As shown in FIG. 6, according to the present embodiment, Li₂CO₃ is usedas an example of a lithium compound.

Further, aggregated trimanganese tetroxide (Mn₃O₄) formed by aggregationof fine primary particles is used as trimanganese tetroxide as amanganese compound. The trimanganese tetroxide (Mn₃O₄) has a primaryparticle diameter according to crystallite size from 50 nm to 150 nm,preferably from 60 nm to 140 nm, and preferably an average secondaryparticle diameter from 3 μm to 20 μm. This is because the primaryparticle diameter being too large or too small is considered to lead todeterioration of high temperature properties of lithium oxide, and theaverage secondary particle diameter being too small is considered tolead to deterioration of high temperature properties of lithium oxide.Further, when average secondary particle diameter is too large, reactionwhen combined with Li deteriorates, and as a result, it is considered tolead to instability in a crystal of lithium manganese oxide.

Note that crystallite size of trimanganese tetroxide was calculated byusing the Rietveld method from powder X-ray diffraction. For X-raydiffraction, measurement was carried out using SmartLab (manufactured byRigaku Corporation) (source: CuKα), and measurement conditions were 10°to 90° in 2θ/θ by 0.02° steps (1.2 s hold scan) at 0.02° increments.

According to the present embodiment, Nb₂O₅, a niobium compound, or MoO₃,a molybdenum compound, is used as an example of a crystal plane growthsuppressor. However, aside from a niobium compound or molybdenumcompound, any element or compound can be used as long as it functions asa crystal plane growth suppressor.

Here, the added amount of the niobium compound or molybdenum compound asthe crystal plane growth suppressor is from 0.1 mol % to 1.2 mol % interms of a metal element with respect to Mn. When the added amount ofniobium compound, molybdenum compound, or the like is less than theabove range, a function as the crystal plane growth suppressor isconsidered to be insufficient, and conversely, when the added amount isgreater than the above range, it is considered that particles of excessmetal element compound inhibit function of the battery using thepositive electrode active material and become a resistance component.The added amount of the crystal plane growth suppressor according to thepresent invention is preferably from 0.2 mol % to 0.9 mol % in terms ofmetal element with respect to Mn.

(ii) Next, the mixture formed by mixing is fired in an oxidizingatmosphere (step S2). Firing temperature is from 700° C. to 950° C., andmore preferably from 730° C. to 900° C.

(iii) Next, positive electrode active material particle powder obtainedby firing is disintegrated (step S3), and passed through a sieve of amesh with mesh openings of 45 μm (step S4), in order to obtain positiveelectrode active material particle powder 10 pertaining to the presentembodiment.

In producing the positive electrode active material particle powder, itis also possible to mix substituted metal element compound together withthe lithium compound, trimanganese tetroxide, and crystal plane growthsuppressor. In this case, as the substituted metal element, at least onemetal element other than Mn, able to substitute at the Mn(16d) site canbe used. By using such a substituted metal element, it is possible tocontrol charge/discharge capacity of a battery, and to further improvecharge/discharge cycle and high temperature properties. As specificexamples, Li, Fe, Ni, Mg, Zn, Al, Co, Cr, Si, Ti, Sn, V, Sb, and thelike can be used as a substituted metal element.

Further, it is preferable that a substituted metal element is uniformlypresent inside the positive electrode active material particles (auniform solid solution). In a case in which a metal element is unevenlydistributed inside a particle, it is considered to deteriorate stabilityin a non-aqueous electrolyte secondary battery.

9. Non-Aqueous Electrolyte Secondary Battery

Configuration of a lithium ion secondary battery 100 according to thepresent embodiment, which is manufactured using the positive electrodeactive material particle powder described above, is described withreference to FIG. 7.

The lithium ion secondary battery 100 pertaining to the presentembodiment includes a tablet-like positive electrode element 1 and anegative electrode element 2 disposed so as to sandwich a separator 3,and is stored inside a package body composed of a positive electrodecase 4 and a negative electrode case 5. The positive electrode case 4 iselectrically connected to the positive electrode element 1, and thenegative electrode case 5 is electrically connected to the negativeelectrode element 2. The positive electrode case 4 and the negativeelectrode case 5, in a state in which a gasket 6 is closely sandwichedtherebetween, are caulked by outer edge portions 4 e, 5 e.

(i) Positive Electrode Element 1

The positive electrode element 1 is formed by using the positiveelectrode active material particle powder 10. A specific method offorming the positive electrode element 1 is omitted because it ispossible to adopt a publicly-known method, but the positive electrodeelement 1 can be formed by adding and mixing a conductive agent and abinder to the positive electrode active material particle powder 10.

As the conductive agent, acetylene black, carbon black, graphite, andthe like can be used, for example. Further, as the binder,polytetrafluoroethylene, polyvinylidene fluoride, and the like can beused.

(ii) Negative Electrode Element 2

The negative electrode element 2 is formed by using a negative electrodeactive material such as lithium metal, lithium/aluminium alloy,lithium/tin alloy, or graphite. In the lithium ion secondary battery 100pertaining to the present embodiment, as one example, Li foil having athickness of 300 μm is used.

(iii) Electrolytic Solution

As a solvent of the electrolytic solution, an organic solvent can beused that contains at least one of a combination of ethylene carbonateand diethyl carbonate, a carbonate such as propylene carbonate ordimethyl carbonate, and an ether such as dimethoxyethane.

As an electrolyte of the electrolytic solution, at least one of lithiumhexafluorophosphate or a lithium salt such as lithium perchlorate orlithium tetrafluoroborate can be used, and this electrolyte is dissolvedin the solvent.

According to the lithium ion secondary battery 100 pertaining to thepresent embodiment, as one example, 1 mol/L of LiPF₆ added tonon-aqueous electrolyte solution (EC:DMC=1:2 ratio) is used.

As shown in FIG. 7, the lithium ion secondary battery 100 pertaining tothe present embodiment is, for example, a 2032 size coin cell. Aninitial discharge capacity of the lithium ion secondary battery 100 isfrom 80 mAh/g to 120 mAh/g. In a case of an initial discharge capacityless than 80 mAh/g, battery capacity is too low for practical use.Further, in a case of an initial discharge capacity greater than 120mAh/g, sufficient stability cannot be ensured for high temperatureproperties. Initial discharge capacity of the lithium ion secondarybattery 100 is preferably from 85 mAh/g to 115 mAh/g.

Further, according to the lithium ion secondary battery 100 pertainingto the present embodiment, high temperature cycle capacity retentionrate is at least 96.5%. A high temperature cycle capacity retention rateof at least 97% is preferable.

Further, the lithium ion secondary battery 100 pertaining to the presentembodiment has a capacity recovery rate of at least 96%. A capacityrecovery rate of at least 96.5% is preferable.

10. Effects

According to the lithium ion secondary battery 100 using the positiveelectrode active material particle powder 10 pertaining to the presentembodiment, it is possible to improve high temperature properties.

In the method for producing the positive electrode active materialparticle powder, when the manganese compound, the lithium compound, andcrystal plane growth suppressor are homogeneously mixed and fired at atemperature from 700° C. to 950° C. in an oxidizing atmosphere (forexample, in air), and resulting particle powder is used in a non-aqueouselectrolyte secondary battery, it is possible to obtain the positiveelectrode active material particle powder 10 capable of improving hightemperature properties.

[Evaluation]

The following describes property evaluation results using specificworking examples.

First, examples and comparative examples used for evaluation aredescribed with reference to Table 1.

TABLE 1 Precursor Mixed composition Average Crystal plane secondarySubstituted Crystal growth Firing conditions particle Crystallite metalplane suppressor Air Mn diameter size Li/(Mn + element growth addedamount temperature Time compound (μm) (nm) Me) Me suppressor (mol %) (°C.) (hours) Example 1 Mn₃O₄ 10.5 92 0.58 — Nb₂O₅ 0.60 820 3 Example 2Mn₃O₄ 10.5 92 0.58 — Nb₂O₅ 0.30 820 3 Example 3 Mn₃O₄ 10.5 92 0.56Al(OH)₃ Nb₂O₅ 0.55 810 3 Example 4 Mn₃O₄ 10.5 92 0.55 MgO Nb₂O₅ 0.55 8103 Example 5 Mn₃O₄ 10.5 92 0.59 — MoO₃ 0.50 820 3 Comparative Mn₃O₄ 10.592 0.58 — — — 820 3 example 1 Comparative Mn₃O₄ 10.5 92 0.58 — Nb₂O₅0.06 820 3 example 2

The positive electrode active material particle powder pertaining toExample 1 was produced as follows.

As shown in Table 1, trimanganese tetroxide (Mn₃O₄) of crystallite size92 nm and average secondary particle diameter 10.5 μm and lithiumcarbonate (Li₂CO₃) were mixed at a ratio of Li/Mn=0.58; Nb as a crystalplane growth suppressor was weighed and mixed as Nb₂O₅ at 0.60 mol %with respect to moles of Mn in trimanganese tetroxide; then fired in anair atmosphere at 820° C. for three hours to produce lithium manganeseoxide particle powder.

As shown in FIG. 5, according to X-ray diffraction, in the resultantpositive electrode active material particle powder, in addition tolithium manganese oxide that can be indexed by Fd-3m, Nb, which is thecrystal plane growth suppressor, was present in LiNbO₃ phase. That is,the positive electrode active material particle powder pertaining toExample 1 had a composition of Li_(1.10)Mn_(1.90)O₄+LiNbO₃.

Further, as a result of SEM image observation of the positive electrodeactive material particle powder pertaining to this example, as shown inFIG. 1A and FIG. 2A, it was confirmed that aggregated particles werecomposed of primary particles forming polyhedral shapes in which a (111)plane is adjacent to a (100) plane.

Further, the resultant positive electrode active material particlepowder had an average primary particle diameter of approximately 0.8 μmand an average secondary particle diameter (D50) of 14.3 μm.

Next, using the positive electrode active material particle powderproduced as described above, a lithium ion secondary battery wasproduced as follows.

By weight, 92% the positive electrode active material particle powder,2.5% acetylene black and 2.5% graphite as a conductive agent, and 3%polyvinylidene fluoride dissolved in N-methylpyrrolidone as a binderwere mixed, coated on Al metal foil and dried at 120° C. A sheetprepared in this way was punched out to a 14 mm diameter, then pressedat 1.5 ton/cm² for use as a positive electrode element.

Metal lithium having a thickness of 300 μm was punched out to a 16 mmdiameter for use as a negative electrode element.

As an electrolytic solution, a solution prepared by mixing 1 mol/L LiPF₆in EC and DMC at a volume ratio of 1:2 was used.

The lithium ion secondary battery according to this example is a 2032type coin cell.

EXAMPLE 2

As shown in Table 1, in the positive electrode active material particlepowder pertaining to Example 2, the added amount of Nb was changed fromthe added amount used in Example 1. Production was otherwise identical.

EXAMPLE 3

The positive electrode active material particle powder pertaining toExample 3 was produced as follows.

As shown in Table 1, trimanganese tetroxide (Mn₃O₄) of crystallite size92 nm and average secondary particle diameter 10.5 μm, lithium carbonate(Li₂CO₃), and aluminium hydroxide (Al(OH)₃) were mixed at a ratio ofLi/(Mn+Al)=0.56; Nb as a crystal plane growth suppressor was weighed andmixed as niobium oxide (Nb₂O₅) at 0.55 mol % with respect to moles of Mnin trimanganese tetroxide; then fired in an air atmosphere at 810° C.for three hours to produce lithium manganese oxide particle powder. Thatis, the positive electrode active material particle powder pertaining toExample 3 had a composition of Li_(1.08)Mn_(1.85)Al_(0.07)O₄+LiNbO₃.

Other elements of the lithium ion secondary battery were the same as inExamples 1 and 2.

EXAMPLE 4

The positive electrode active material particle powder pertaining toExample 4 was produced as follows.

As shown in Table 1, trimanganese tetroxide (Mn₃O₄) of crystallite size92 nm and average secondary particle diameter 10.5 μm, lithium carbonate(Li₂CO₃), and magnesium oxide (MgO) were mixed at a ratio ofLi/(Mn+Mg)=0.55; Nb as a crystal plane growth suppressor was weighed andmixed as niobium oxide (Nb₂O₅) at 0.55 mol % with respect to moles of Mnin trimanganese tetroxide; then fired in an air atmosphere at 810° C.for three hours to produce lithium manganese oxide particle powder. Thatis, the positive electrode active material particle powder pertaining toExample 4 had a composition of Li_(1.06)Mn_(1.89)Mg_(0.05)O₄+LiNbO₃.

Other elements of the lithium ion secondary battery were the same as inExamples 1, 2, and 3.

EXAMPLE 5

The positive electrode active material particle powder pertaining toExample 5 was produced as follows.

As shown in Table 1, trimanganese tetroxide (Mn₃O₄) of crystallite size92 nm and average secondary particle diameter 10.5 μm, lithium carbonate(Li₂CO₃), molybdenum oxide (MoO₃) at 0.50% of Mo to moles of Mn intrimanganese tetroxide as a crystal plane growth suppressor were weighedand mixed at a ratio of Li/(Mn+Mo)=0.59; then fired in an air atmosphereat 820° C. for three hours to produce lithium manganese oxide particlepowder. Composition of the positive electrode active material particlepowder pertaining to Example 5 is Li_(1.11)Mn_(1.89)Mo_(0.01)O₄.

Other elements of the lithium ion secondary battery were the same as inExamples 1, 2, 3, and 4.

As a result of SEM image observation of the positive electrode activematerial particle powder pertaining to this example, as shown in FIG. 2Cand FIG. 2D, it was confirmed that aggregated particles were composed ofprimary particles forming polyhedral shapes having a (100) plane and a(110) plane in addition to a (111) plane.

COMPARATIVE EXAMPLE 1

As shown in Table 1, in production of the positive electrode activematerial particle powder pertaining to Comparative example 1, Nb, whichis a crystal plane growth suppressor, is not added. Composition of thepositive electrode active material particle powder pertaining toComparative example 1 is Li_(1.10)Mn_(1.90)O₄.

Other production conditions are the same as in Example 1.

COMPARATIVE EXAMPLE 2

As shown in Table 1, in production of the positive electrode activematerial particle powder pertaining to Comparative example 2, incontrast to Example 1, an added amount of Nb is 0.06 mol % with respectto moles of Mn in trimanganese tetroxide. Other production conditionsare the same as in Example 1. Composition of the positive electrodeactive material particle powder pertaining to Comparative example 2 isLi_(1.10)Mn_(1.90)O₄+LiNbO₃.

As a result of SEM image observation of the positive electrode activematerial particle powder pertaining to Comparative example 2, it wasconfirmed that for primary particles exposed on surfaces of secondaryparticles, 55% of the primary particles formed polyhedral shapes inwhich a (111) plane is adjacent to at least one (100) plane.

Lithium ion secondary batteries produced as described above wereevaluated as follows.

(Capacity Recovery Rate)

With respect to capacity recovery rate indicating high temperatureproperties, the lithium ion secondary batteries were charged to 4.3 V ata 0.1 C-rate of current density (constant current, constant voltage,(CC-CV)), then discharged to 3.0 V (constant current (CC)). Let thedischarge capacity at that time be “a”.

Subsequently, the lithium ion secondary batteries were charged again to4.3 V at a 0.1 C-rate of current density (CC-CV), removed from acharge/discharge device, and left for six weeks in a constanttemperature bath at 60° C. After six weeks the lithium ion secondarybatteries were removed from the constant temperature bath, attached to acharge/discharge device, discharged at a 0.1 C-rate (CC) to 3.0 V,charged to 4.3 V (CC-CV), and discharged to 3.0 V (CC). Let thedischarge capacity at that time be “b”.

Then, (b/a×100) was taken as the capacity recovery rate (%). Results areshown in Table 2.

TABLE 2 Battery properties Initial discharge Capacity High temperaturecycle Rate Positive electrode active capacity recovery rate capacityretention rate property material composition (mAh/g) (%) (%) (%) Example1 Li_(1.10)Mn_(1.90)O₄ 105.9 97.9 98.2 94.9 Example 2Li_(1.10)Mn_(1.90)O₄ 105.4 97.6 97.8 94.2 Example 3Li_(1.08)Mn_(1.85)Al_(0.07)O₄ 104.8 98.8 98.0 94.1 Example 4Li_(1.06)Mn_(1.89)Mg_(0.05)O₄ 105.1 98.1 98.2 95.1 Example 5Li_(1.11)Mn_(1.89)Mo_(0.01)O₄ 106.3 97.1 97.5 96.1 ComparativeLi_(1.10)Mn_(1.90)O₄ 105.7 94.9 94.6 94.1 example 1 ComparativeLi_(1.10)Mn_(1.90)O₄ 105.8 95.5 95.5 93.9 example 2

(High Temperature Cycle Capacity Retention Rate)

For high temperature cycle capacity retention rate indicating hightemperature properties, the lithium ion secondary batteries were chargedfrom 3.0 V to 4.3 V at a C-rate of 0.5 (CC-CV), then discharged to 3.0 Vat a C-rate of 1.0 (CC). Let the discharge capacity at that time be “c”.

Subsequently, charging and discharging between 3.0 V and 4.3 V wasrepeated for 40 cycles (charging at a C-rate of 0.5 at CC-CV,discharging at a C-rate of 1.0 at CC), and discharge capacity at the41st cycle is defined as “d”.

Then, (d/c×100) was taken as the high temperature cycle retention rate(%). Results are shown in Table 2.

(Rate Property)

For rate properties, between 3.0 V and 4.3 V in a 25° C. environment,charging was performed at a C-rate of 0.1 (CC-CV) and when dischargingat a C-rate of 0.1 or 10 (CC), discharge capacity at the C-rate of 0.1is defined as “e” and discharge capacity at the C-rate of 10 is definedas “f”.

Then (f/e×100) was taken as the rate property (%). These results arealso shown in Table 2.

(Discussion 1)

First, as shown in Table 2, regarding capacity recovery rate,Comparative example 1 has a value of 94.9% and Comparative example 295.5%. In contrast, Example 1 has a value of 97.9%, Example 2 97.6%,Example 3 98.8%, Example 4 98.1%, and Example 5 97.1%, which are highervalues than those of the comparative examples.

FIG. 8A shows capacity recovery rates of Example 1 and Comparativeexample 1. As shown in FIG. 8A, added Nb, which is a crystal planegrowth suppressor, reduces area of a (111) plane, in which Mndissolution is considered to be greater, and increases area of a (100)plane, which is considered to be strong against Mn dissolution, andtherefore capacity recovery rate (storage property in high temperature)achieves an improvement of approximately 3%.

(Discussion 2)

As shown in Table 2, regarding high temperature cycle capacity retentionrate, Comparative example 1 has a value of 94.6% and Comparative example2 95.5%. In contrast, Example 2 has a value of 97.8%, Example 5 97.5%,and Examples 1, 3, 4 at least 98%. As shown in FIG. 8B, it can be seenthat the high temperature cycle capacity retention rate of Example 1 isapproximately 2% better than that of Comparative example 1.

(Discussion 3)

As shown in Table 2, with respect to rate properties, Comparativeexample 1 has a value of 94.1% and Comparative example 2 93.9%. Incontrast, Examples 1, 2, 4 show higher values, and it is considered thatExample 5, which has a large area of (110) plane having Li diffusionchannels, exhibits a significantly higher rate property than Comparativeexample 1.

SUMMARY

Positive electrode active material particle powder for a non-aqueouselectrolyte secondary battery pertaining to Examples 1-5 is positiveelectrode active material particle powder comprising: lithium manganeseoxide particle powder having Li and Mn as main components and a cubicspinel structure with an Fd-3m space group, wherein the lithiummanganese oxide particle powder is composed of secondary particles,which are aggregates of primary particles, an average particle diameter(D50) of the secondary particles being from 4 μm to 20 μm, and at least80% of the primary particles exposed on surfaces of the secondaryparticles each have a polyhedral shape in which each (111) plane thereofis adjacent to at least one (100) plane thereof.

Next, the relationship between surface energy and Mn dissolution isdescribed with reference to FIG. 9A, FIG. 9B, and Table 3.

TABLE 3 Crystal plane (100) (111) Surface energy γ (J/m²) 0.96 1.29 Mndissolution Gibbs energy (kcal/mol) 27.6 −16.1

Note that this discussion is made in contrast with the prediction fromthe results of surface energy and Mn dissolution reaction Gibbs energychange from simulation performed by Thackeray, IMLB 2010 (InternationalMeeting on Lithium Batteries, summer 2010).

As shown in FIG. 9A, for a particle that has a (100) plane and (111)planes in an initial state, it can be observed that etching of theparticle greatly corrodes the (111) planes, as shown in FIG. 9B. Incontrast, corrosion of the (100) plane is not as great as that of the(111) planes.

Here, positive electrode active material particle powder shown in FIG.9B was obtained by etching under the following conditions. Starting with3 ml of a solution in which 1 mol/L of LiPF₆ was used as a solute andethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in avolume conversion ratio of 3:7, 2 g of positive electrode activematerial particle powder was mixed with the solution, the mixture wassealed and left for 1 week in an environment of 80° C. Subsequently, themixture was filtered, powder was washed with dimethyl carbonate (DMC)then dried, in order to obtain etched positive electrode active materialparticle powder.

As shown in Table 3, surface energy γ of a (100) plane was 0.96 J/m²,while that of a (111) plane was 1.29 J/m², the (111) plane having agreater surface energy. Further, Mn dissolution Gibbs energy of a (100)plane was 27.6 kcal/mol and Mn dissolution Gibbs energy of a (111) planewas −16.1 kcal/mol, indicating that dissolution of Mn is more likely toproceed in the (111) plane.

Based on the above results, a degree of corrosion progression in the SEMimage shown in FIG. 9B is greater in (111) planes than (100) planes,which is consistent with Thackeray. From these results, when consideringthat low Mn dissolution at high temperatures and good storage propertiesat high temperatures are equivalent results, the above prediction isconsistent with the results of battery properties found in the presentembodiment.

[Other Configurations]

In Example 3, Li and Al were used as substituted metal elements, and Liand Mg were used as substituted metal elements in Example 4, butsubstituted metal elements are not limited to these examples. Forexample, a part of Mn may be substituted with one or more cationsselected from metal elements capable of substituting at the 16d site,such as Fe, Ni, Zn, Co, Cr, Si, Ti, Sn, V, or Sb.

According to the Embodiment, Nb and Mo are taken as examples of crystalplane growth suppressor used in producing the positive electrode activematerial particle powder, but the present invention is not limited tothese examples. Any material capable of suppressing growth of crystalplanes other than (111) planes can be adopted.

Further, according to the Embodiment, a coin type of lithium ionsecondary battery is used as an example of a non-aqueous electrolytesecondary battery, but the present invention is not limited to thisexample. For example, the present invention can be applied tocylindrical non-aqueous electrolyte secondary batteries, rectangularnon-aqueous electrolyte secondary batteries, and the like. Further, thenegative electrode element, the separator, the electrolytic solution,and the like may be changed appropriately.

INDUSTRIAL APPLICABILITY

The present invention is applicable to the realization of non-aqueouselectrolyte secondary batteries having excellent high temperatureproperties.

REFERENCE SIGNS LIST

1. Positive electrode element

2. Negative electrode element

3. Separator

4. Positive electrode case

5. Negative electrode case

6. Gasket

10. Positive electrode active material particle powder

100. Lithium ion secondary battery

The invention claimed is:
 1. Positive electrode active material particlepowder for a non-aqueous electrolyte secondary battery, the positiveelectrode active material particle powder comprising: lithium manganeseoxide particle powder having Li and Mn as main components and a cubicspinel structure with an Fd-3m space group, wherein the lithiummanganese oxide particle powder is composed of secondary particles,which are aggregates of primary particles, an average particle diameter(D50) of the secondary particles being from 4 μm to 20 μm, and at least80% of the primary particles exposed on surfaces of the secondaryparticles each have a polyhedral shape in which each (111) plane thereofis adjacent to at least one (100) plane thereof, and in X-raydiffraction analysis of the positive electrode active material particlepowder, a cubic spinel phase composed of Li and Mn, and a phase of acompound of Nb and Li, or Mo and Li are present.
 2. The positiveelectrode active material particle powder of claim 1, wherein one ormore metal elements other than Mn are substituted at an Mn(16d) site,and when Me denotes a metal element other than Li among the one or moremetal elements, an [Li/(Mn +Me)] ratio is from 0.5 to 0.65.
 3. Anon-aqueous electrolyte secondary battery comprising: a positiveelectrode element that includes the positive electrode active materialparticle powder of claim 1.